Chemicals from the hydrosphere

Fortunately for the mining industry, the composition of the crust is not uniform. Natural forces have concentrated different minerals in different places. For example, as molten rock gradually cools, the minerals that sohd-ify first (those with the higher melting points) can sink in the remaining hq-uid and become concentrated. Or minerals can be redistributed according to variations in their solubility in natural waters. 

The western United States was once covered by a large, landlocked sea. The water evaporated, leaving huge deposits of sodium carbonate, a soluble salt that is a valuable chemical raw material. While most nations must manufacture sodium carbonate from other chemicals, the United States meets a large proportion of its needs by mining. Other minerals are concentrated elsewhere, of course. Most of the known deposits of nickel are in New Caledonia and Zimbabwe. Most of the chromium is in Botswana and Turkey. Each country must rely on imports of one kind or another. 

Minerals have definite internal structure and chemical composition. Most of Earfh s crusf consists of rocks, which may be single minerals or mixtures of minerals. A nafural material that contains a sufficient concentration of an elemenf or compound to economically justify mining it is an ore. 

Some other uses for sodium chloride include food processing highway snow melting animal feed domestic table salt and rubber, oil. paper, and textile manufacture. 

Separation of salt from seawater by evaporation in San Francisco Bay. 

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